Сonformational study of persulfated propyl glucuronide

Glucuronic acid is an important constituting block of biologically active glycosaminoglycans where it can be present in non-sulfated, mono-sulfated and di-sulfated forms. Despite that some investigators reported previously that the exhaustively sulfated glucuronic acid moiety was characterized with unusual ¹H-¹H coupling constants and some times chemical shifts, these were just qualitative studies in which their authors suggested that the mentioned deviations in NMR spectra might mean complete inversion of the normal D-pyranoside chair conformation ⁴C₁ to ¹C₄. Herein we outline a detailed conformational investigation showing that the distortion in the pyranoside ring of the persulfated glucuronic acid cannot be described simply with ⁴C₁↔¹C₄ inversion. Instead, the experimental NOE data clearly indicate that two skew-boat conformers, ^OS₂ and ³S₁, provide significant contribution to the conformational equilibrium.